In an electric vehicle (EV) or a hybrid electric vehicle (HEV) to be a vehicle using electric energy for an entire portion or a part of traveling power, a motor driving a traveling battery and tires is installed. When driving force is given to the tires, the motor converts electric energy of the battery into kinetic energy and consumes the kinetic energy. However, when braking force is given to the tires, the motor converts the kinetic energy into the electric energy and can charge the battery. An operation of the latter is referred to as energy regeneration (hereinafter, referred to as regeneration). Meanwhile, in friction braking in which the kinetic energy is converted into thermal energy, energy that becomes heat once and is radiated in the air cannot be reused. For this reason, in the EV or the HEV, to perform braking by regeneration as much as possible leads to energy saving.
In the vehicle, because the tires should generate braking/driving force and lateral force for turning, stable turning may be disabled when strong braking is performed. Even in this case, when the friction braking is performed, it is possible to perform control to generate the targeted braking force in a state in which the highest priority is given to stability of a vehicle behavior. However, when weight is laid on recovering of the energy by the regeneration, the vehicle behavior may be unstable.
Particularly, in a configuration of a driving system in which wheels driven by the motor enabling the regenerative braking are only two front wheels or two rear wheels, restrictions of the regenerative braking become remarkable to maintain the stability of the vehicle behavior.
As associated technology of this technical field, there is Patent Literature 1. In Patent Literature 1, a method of controlling regenerative braking force to correspond to a slip ratio of the wheels is disclosed.
In addition, there is Patent Literature 2 as technology becoming the basis of the present application. In Patent Literature 2, the regenerative braking is not premised, but a control method using a ratio of the wheel slip ratio to the braking force to maintain the stability of the vehicle behavior with an appropriate margin is disclosed.